How does that work? The 401(k) providers are lending out the securities that their customers own?

No, 401k admins do not own the securities, the employees do. The comment is incorrect in implying the government bailed out the administrators, but the government did backstop the price the securities (the stock market) itself.

Hence why I think an SP500 investment is risk free on a >3 year timeline.

The 401(k) money is held separately from the company funds.

> many of the companies that provide 401(k) were on the verge of collapse in 2008.

The stock market went to shit, not the providers. The 401k appeal is that it's an account you *own* and the government can't touch for money, it would be the same as expropriating a bank account, which to be fair, the Argentinian goverment kind of did in 2001, hence why since then, people there save money in usd cash or in a foreign account, not in the local financial system. If the US government has to expropriate or do weird stuff in general with 401k accounts, we are in a situation where shit hit the fan long ago.

Ask Cypriots about bank account haircuts :-)

I'm from Argentina, the government there did that before it was cool

"You can always lose your money."

It went somewhere.